Voice-band modems: A device to transmit data over telephone networks

Over the last 40 years, there has been continuous evolution in the design of voice-band modems-starting at a data rate of 300 bits per second in late 1950s, a rate of 33,600 bits per second has been achieved in 1995. Realising such high data rates over the voice band of 3400 Hz is a remarkable feat made possible by combining sophisticated techniques from three disciplines, communication theory, signal processing and information theory. In this article, we begin with a brief introduction of voice-band modems and then introduce the basic principles of data transmission.